The US has imposed "sweeping" sanctions on officials in a Syrian government agency in response to a suspected chemical attack earlier this month.

The treasury department ordered a freeze on all assets in the US of 271 employees of the Syrian Scientific Studies and Research Centre (SSRC).

The US believes it made the nerve agent that killed more than 80 people in the rebel-held town of Khan Sheikhoun.Syria says the incident was a fabrication.

President Bashar al-Assad has accused the West of making up events in Khan Sheikhoun on 4 April so the US had an excuse to carry out missile strikes on the government's Shayrat airbase, which took place a few days after the alleged attack.

In a statement on Monday, the treasury department said the 271 employees had been responsible for developing and producing non-conventional weapons and the means to deliver them".

The sanctions mean that American citizens will be forbidden from having any dealings with them.

Treasury Secretary Steven Mnuchin said that "these sweeping sanctions target the scientific support centre for Syrian dictator Bashar al-Assad's horrific chemical weapons attack on innocent civilian men, women, and children."The United States is sending a strong message with this action that we will hold the entire Assad regime accountable for these blatant human rights violations in order to deter the spread of these types of barbaric chemical weapons."

Witnesses have said they saw warplanes attack Khan Sheikhoun - but Russia, a key ally of President Assad, says a rebel depot of chemical munitions was hit.

Footage showed victims - many of them children - convulsing and foaming at the mouth. Sufferers were taken to hospitals across the border in Turkey.

The Organisation for the Prohibition of Chemical Weapons (OPCW) has said that allegations of a chemical attack were "credible" based on a preliminary examination of the evidence.

More than 300,000 people have lost their lives and millions of people have been displaced since a peaceful uprising against President Assad six years ago turned into a full-scale civil war.

U.S. Imposes Sanctions on Syrian Government Workers After Sarin Attack

WASHINGTON — The Trump administration on Monday imposed sanctions on 271 employees of the Syrian government agency it said was responsible for producing chemical weapons and ballistic missiles, an effort to impose a sweeping punishment after a sarin attack on civilians this month.

The sanctions on members of President Bashar al-Assad’s Scientific Studies and Research Center more than doubles the number of Syrian individuals and entities whose property has been blocked by the United States and who are barred from financial transactions with American people or companies.

Steven Mnuchin, the secretary of the Treasury, described it as one of the largest actions his department’s Office of Foreign Assets Control had ever undertaken. It seeks to punish those behind this month’s chemical weapons attack in Khan Sheikhoun and previous ones carried out by Mr. Assad’s government, and to deter others contemplating similar actions.

“The United States is sending a strong message with this action that we will not tolerate the use of chemical weapons by any actor, and we intend to hold the Assad regime accountable for its unacceptable behavior,” Mr. Mnuchin told reporters at the White House. “The Treasury Department, together with the Department of State and our international partners, will continue to relentlessly pursue and shut down the financial networks of any individuals involved with Syria’s production or use of chemical weapons.”

It is not clear what impact the restrictions will have, given that they only apply to business, financial holdings or transactions involving United States people or companies. Administration officials said they had focused on highly educated Syrian officials with deep expertise in chemistry who were thought to have the ability to travel extensively and possibly to use the American financial system.

“We wouldn’t be doing this if we didn’t think it was impactful,” Mr. Mnuchin said. “It’s quite impactful.”

It was the second time the United States government has imposed sanctions on Syrians for the government’s use of chemical weapons. In January, the Treasury Department blacklisted 18 Syrians, including six connected to the scientific studies center, after an investigation by the Organization for the Prohibition of Chemical Weapons, the international body that polices chemical weapons, determined that the government had been responsible for three chlorine gas attacks.

The Syrian government has portrayed the Scientific Studies and Research Center as a medical and agricultural study agency, but the United States government has long considered it a training ground and secret laboratory network for engineers developing chemical and biological weapons.

Britain applauded the American action, calling it a strong message that the use of chemical weapons is unacceptable.

“The abhorrent attack on Khan Sheikhoun is a stark reminder that the international community must work together to deter the future use of chemical weapons in any circumstances,” Boris Johnson, the British foreign secretary, said in a statement. “Sanctions send a clear signal that actions have consequences and seek to deter others from a similar acts of barbarism.”

Syria agreed in a 2013 deal brokered by Russia to destroy its chemical weapons arsenal and get rid of material that could be used to resume the manufacture of such weapons.

But American officials have said this month’s attack indicated that the Assad government still had the capacity to make and use chemical weapons.

On Monday, one official said that assault and at least one other this month suggested that Syria had an ongoing chemical weapons program and called into question declarations the government had made to the contrary.

Republicans who had long criticized the Obama administration for doing too little to prevent the Assad regime’s atrocities also praised the sanctions.

“They represent another stark departure from the Obama administration’s dithering on Syria, which only worsened the bloodshed and created a vacuum for ISIS,” said Representative Ed Royce, Republican of California and the chairman of the Foreign Affairs Committee, referring to the Islamic State. He said he would push forward with Democrats on legislation that would “give the White House additional leverage to hold Assad — as well as his Russian and Iranian backers — accountable.”

A report issued by the National Security Council this month that included a declassified account of the Khan Sheikhoun attack said American intelligence had indicated that “personnel historically associated with Syria’s chemical weapons program” were at Shayrat airfield in March and on the day of the assault.

That airfield is believed to have been used by Syrian government warplanes to carry out the attack. President Trump ordered missile strikes on the airfield days later.

An administration official declined to say whether any of those figures were part of the group targeted with sanctions on Monday, citing the need to protect intelligence sources and methods, but asserted that those being blacklisted were believed to be responsible for attacks.

US imposes new sanctions on Syrian officials over chemical attack

The US has issued sanctions against hundreds of Syrian scientists and officials for their role in developing chemical weapons. The measures come after a poison gas attack killed over 80 people in a rebel-held province.

The Trump administration blacklisted hundreds of employees of a Syrian government agency on Monday for what Treasury Secretary Steven Mnuchin said was the use of sarin gas on civilians in early April.

The measures target 271 employees of Syria's Scientific Studies and Research Center (SSRC), making it one of the US Treasury's largest sanctions announcements.

All of the employees have expertise in chemistry or related fields and have worked or been involved in the chemical weapons program since 2012, said a US Treasury statement.

The sanctions include a freeze on all US assets and block any American business or person from dealing with them.

The British government welcomed US sanctions on Monday, saying the sanctions sent a signal that "actions have consequences."

"Sanctions send a clear signal that actions have consequences and seek to deter others from similar acts of barbarism. We welcome the role sanctions play in increasing pressure on the Syrian regime to turn away from its military campaign," Foreign Minister Boris Johnson said in a statement.

Targeting science centerThe US said the SSRC was responsible for developing the chemical weapon used in the April 4 attack in the rebel-held province of Idlib. The attack left 87 people dead in the town of Khan Sheikhun, including many children, prompting outrage from Western countries.

Washington has said Assad's forces carried out the attack while Assad has said the attack is a "fabrication" by the West.

Although the Syrian government maintains that the SSRC is a civilian research center, "its activities focus substantively on the development of biological and chemical weapons," US officials said.

Former US President George W. Bush issued the first sanctions against the SSRC in 2005, accusing it of producing weapons of mass destruction.

Under President Barack Obama, the United States sanctioned people and companies for supporting the SSRC in July 2016. And prior to Trump taking office, the Treasury sanctioned six SSRC officials on January 12, saying the officials were affiliated with chemical weapons research programs.

Steps against Syrian governmentThe US Treasury's move to sanction SSRC employees follows the US military's firing 59 Tomahawk cruise missiles at a Syrian airfield on April 7. The Pentagon said the Syrian government air base was used to launch the chemical attack.

The attack was also debated in the United Nations Security Council. A resolution demanding the Syrian government's cooperation with an investigation of the attack was vetoed by Russia, a close ally of Assad, on April 12.